If I've acclimated - a very dry, breezy mid-30's (C) or mid-90's (F) is still workable, if not optimal, for work with minimal physical exertion.

Humidity matters a lot. Get a dehumidifier. The cheapest electrical dehumidifiers are air-conditioning.

If i'm lifting equipment, moving desks, that sort of thing... 20c, at 25c im going to be soaked from sweat.

If im working with hot work, like welding or some foundry or greenhouse, probably same idea around 20c. 25c will be too hot to deal with it.